A plasma,etching apparatus is utilized during the process of manufacturing a semiconductor device in the prior art. In the processing chamber of the apparatus, an upper electrode and a lower electrode are set facing opposite each other. In the plasma etching apparatus adopting this structure, the processing gas introduced into the processing chamber is raised to plasma when high-frequency power is applied to the lower electrode and the workpiece placed on the lower electrode, such as a semiconductor wafer (hereafter referred to as a “wafer”) becomes etched. In addition, the lower electrode is internally provided with a temperature control mechanism to adjust the wafer temperature. The lower electrode is also provided with a ring body. The ring body is constituted of an inner ring body and an outer ring body. The inner ring body is set so as to encompass the outer edges of the wafer placed on the lower electrode. The outer ring body is set so as to encompass the periphery of the inner ring body.
The inner ring body is constituted of a conductive material. Thus, the external diameter of the wafer can be made to appear electrically large relative to the plasma during the plasma processing. As a result, the plasma is admitted to the entire wafer in an even manner including the outer edges of the wafer as well as the central area. The outer ring body is constituted of an insulating material. Thus, the plasma becomes concentrated on the wafer during the plasma processing so that the plasma can be evenly guided over the entire wafer surface.
However, the conductive inner ring body where intense ion collisions occur, as at the wafer, becomes heated very easily. In addition, the inner ring body is set above the lower electrode unlike the outer ring body which is directly secured to the lower electrode. As a result, since the heat of the inner ring body cannot be fully radiated to the lower electrode in the pressure reduced atmosphere during the processing, the temperature of the inner ring body becomes high. This results in an inconsistent radical concentration in the vicinity of the inner ring body, to reduce the etching rate at the outer edges of the wafer adjacent to the inner ring body. In addition, a discrepancy in the processing is created between the center of the wafer and the outer edges of the wafer and it becomes difficult to achieve uniform processing over the entire wafer surface.
Technologies for processing wafers having a large diameter, e.g., 300 mm, have been proposed in recent years. The processing area at the outer edges of the wafer increases in proportion to the diameter of the wafer. Consequently, the reduction in yield is further exacerbated unless uniform processing is achieved at the outer edges of the wafer, as described above. In addition, in order to improve the productivity of semiconductor element manufacturing, it is necessary to form elements as close to the outer edges of the wafer as possible. However, this technical requirement cannot be satisfied unless uniform processing is achieved at the outer edges of the wafer.
Furthermore, the rate at which ions in the plasma collide with each other at the insulating outer ring body is a lower than the collision rate at the inner ring body. Thus, the temperature of the outer ring body rises more slowly than the temperature at the inner ring body. As a result, when performing continuous processing, the temperature at the outer ring body in particular, is not stable, after the start of processing until a specific number of wafers have been processed. If the temperature at the outer ring body is unstable, the radical concentration at the periphery of the outer ring body, e.g., at the area encompassing the outer edges of the wafer, becomes inconsistent. Consequently, uniform processing is not achieved at the center of the wafer and at the outer edges of the wafer, resulting in difficulty in performing uniform processing over the entire wafer surface. This necessitates processing to be performed on a specific number of dummy wafers until the temperature of the outer ring body becomes stabilized. Thus, the throughput is reduced.